GB1502362A - Supply circuit for a television receiver - Google Patents

Abstract

1502362 Converting circuits for television receivers INDESIT INDUSTRIA ELETTRODOMESTICA ITALIANA SpA 5 Feb 1975 [6 Feb 1974] 4836/75 Heading H2F A supply circuit for a TV receiver comprises a rectifier 3, smoothing capacitor 7 and a chopper 6 controlled by fly-back pulses from the EHT transformer 10. The transformer 10 is arranged (e.g. by third harmonic tuning) so that the ratio of average voltage across the chopper 6 to the crest value is greater than 0À85. This arrangement reduces the dissipation in the chopper 6. As described, the chopper 6 is driven by fly-back pulses induced in winding 9 of the EHT transformer 10 after differentiating at 12. The output from chopper 6 is passed via resistor 8 and diode 22 (which protects transistor 6 against over voltage) to the primary 27 of the EHT transformer 10 and then to a smoothing capacitor 37 which provides a voltage at 36 which is used for other stages The flyback pulses in winding 9 are also peak rectified at 18 so as to feed D.C. to the base of transistor 11 which modifies the action of chopper 6 so as to stabilize the output against variation in the A.C. supply. A feedback resistor 23 gives further improvement in the relationship between beam current and EHT voltage. The Specification shows the reduction in dissipation in transistor 6 achieved by tuning transformer 10 to the third harmonic rather than the fifth harmonic in known arrangements.